1. Field of the Invention
The present invention relates to a data transmission method in which a data signal is transmitted between a transmitter and receiver in the form of a data stream of data bursts in at least two transmission modes, in the first mode a reference signal being transmitted by the transmitter in each data burst, and in the second mode no reference signal being transmitted by the transmitter in each data burst.
Although applicable in principle to any data transmissions, the present invention and the problem underlying it are described with reference to a cellular CDMA data transmission system (CDMA=Code Division Multiple Access), which uses both a transmission mode which requires the transmission of a reference signal as well as one which does not require a reference signal.
2. Description of Related Art
In transmitting data over multipath channels, the transmitted data symbols create interference at the receiver. The interference can be eliminated in the receiver if the pulse response of the channel is known, such as can be inferred from K. D. Kammeyer, “Communication Transmission,” Second Edition, Information Technology Series, Teubner, Stuttgart, 1996, and from A. Klein, G. K. Kaleh, and P. W. Baier, “Zero Forcing and Minimum Mean-Square-Error Equalization for Multiuser Detection in Code Division Multiple Access Channels,” IEEE Transportation Vehicle Technology, Volume 45 (1996), 276-287. The channel pulse response can be computed, e.g., in the receiver from a received reference signal. However, interference can also be eliminated in the transmitter if the channel pulse responses are known there. Then the channel pulse response no longer needs to be computed in the receiver. In other words, transmission of a reference signal is then not necessary.
It is also possible to combine transmission systems that have interference elimination in the receiver and systems that have elimination in the transmitter, as is known from Bosch, “Mixed Use of Joint Predistortion and Joint Detection in the UTRA TDD mode,” ETSI Tdoc SMG2 UMTS-L1 205/98.
Because in data transmission systems that support interference elimination both in the receiver and in the transmitter the transmitted reference signal is superfluous when elimination is performed by the transmitter, the transmitted reference signal then occupies transmission capacity unnecessarily. If, when elimination is performed by the transmitter, an individualized transmission format is used, then the corresponding transmission devices are more complex (e.g., as a result of the channel coding designs that become necessary) and/or the data services of the two transmission modes are different.